Hi all...new to the forum...hoping someone has a solution for me;

I was running Cubase SX3 for ages with the HDSP 9632 and a Steinberg Midex 8 on Windows XP...no problems; I was using my Roland JD800 as a master keyboard plumbed into the HDSP beakouts plus 9 other synth units....two of which are chained on one output (via midi thru). I had no probs at all....the computer itself was getting ancient though (!) and I have recently purchased from a music colleague a Pentium 4/Asus m/board computer into which I have installed the HDSP card etc...and updated the drivers as insructed ( I believe!)....ditto with the Midex 8.
The card (HDSP) seems to be working fine for audio as I have recorded a short few bars from the JD800 via a Yamaha O2R mixer...and all seems fine. It plays back ok.....
But, I can get no midi in (or out, apparently) in Cubase 5. When the studio computer is first powered up, the Midex (powered from USB port) sits with a red light 'on', on port 1 (input) as I think was normal before.
As soon as Cubase is running its start up procedures, the red light on port 1 goes out...I assume this is part of the problem? Or a symptom...

Please, if anyone can help me out here as I can't 'live' without my midi connections...ok, I'm living in the past ) But the system worked fine before so I don't really understand why, when 'up-grading'...it don't work!! (I'm not the most technically proficient guy in town...so in simple terms please )
Cheers, John D xx